Exhaust, Gas and Pollution The teacher will demonstrate how bromthymol blue is used to indicate presence of CO2 in gas.(refer to sequence below) Following this demonstration, the students will design their own experiments to test gasses which are suspected of containing CO2. A variety of sources should be encouraged by the teachers.(i.e. exhaust from different types of cars, smoke, cigarette smoke, wood stoves natural gas.) A variety of testing procedures should also be encouraged. (Objective 1, inquiry lesson)